ORANGE — Breana Kay McDonald, 2, the cherubic toddler whose battle against leukemia was chronicled in a Times story in December, died early Thursday morning when respiratory problems and other complications overwhelmed her fragile immune system.

Many of Breana's 788 days of life were spent in wards at the Children's Hospital of Orange County. She was born Jan. 4, 1993, with Down's syndrome and a hole in her heart. Seizures, infections and two rounds of open-heart surgery all came in her first 12 months. In her second year, doctors found the early stages of leukemia creeping through her system.

Her parents, Frank and Jan McDonald of Tustin, had hoped a bone marrow transplant Breana received last month might stave off the cancer's progress, but in the end, there were too many medical challenges for her to overcome.

"It took me a long time to let go," said Frank, 34, a Marine. "I'm still bawling my eyes out because I'm going to be missing all the times we could have shared together. But now there'll be no more operations, no more poking and prodding. She's happy and whole now, in heaven, sitting on Christ's knee.

"That's what comforts me. That's where our relief comes from."

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Late last year, doctors had hoped to use a cutting-edge medical technique to provide Breana with the bone marrow transplant that might save her. When Jan McDonald gave birth Nov. 1 to her second daughter, Mariana, a team of specialists was on hand to collect and freeze the rich, marrow-producing blood left in the umbilical cord.

Cord blood had been used in about six dozen cases worldwide as a substitute for traditional bone marrow transplants. The McDonalds, weary and battered by their first daughter's plight, seized on the high-tech miracle-in-the-making to buoy their hopes.

They were enthusiastic about the new procedure's benefits. Doctors said it would eliminate the often-lengthy search for a donor and would lower chances of rejection--and the McDonalds began to envision a day when they would have two healthy daughters.

The dazzling promise of the technology fell flat, though, when the cord blood was screened. Doctors were not satisfied with the DNA match, so the McDonalds would have to turn to the traditional search for a suitable donor. Worse, the leukemia began surging through Breana's system. She spent Christmas and her birthday undergoing chemotherapy and suffering its painful side effects.

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The emotional roller coaster was not over. Another teasing hope was offered in January, when a suitable donor was found relatively quickly and a transplant was scheduled. The Feb. 18 transplant was a success, but only a partial one: Breana had her new marrow, but her health was too poor to sustain her through the trying follow-up doses of chemotherapy needed to eliminate the leukemia.

Respiratory problems dogged her through the end of the month. She was breathing, but her lungs were not getting enough of the oxygen to her blood stream. Breana was put on a high-power ventilator, but by late Wednesday night, the pressure the device exerted on her lungs and heart began to be too much.

Doctors said the pressure would continue to mount until her heart gave way. Breana, her body swollen and in pain, was living only by the pulse of a machine, so, just before the dawn of a rainy Thursday morning, her parents made the decision to end the suffering.

"It was terrible at the end, she look so bad, with the swelling," Jan, 25, said. "It was hard to see her that way. But it was still hard to say goodby."

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Breana is survived by her parents; her sister, Mariana; her stepsister, Tasandra McDonald; and her grandparents, Dennis and Mynda McDonald of Spartanburg, S.C., and Gordon and Kay Schippy of Atlanta. A memorial service is scheduled for 2 p.m. Sunday at the Reorganized Church of Jesus Christ of Latter Day Saints, 395 S. Tustin Ave., Orange.

In lieu of flowers, the family asked well-wishers to send donations in Breana's name to the Irvine Children's Education Center ((714) 509-9050), or the Ronald McDonald House, 383 S. Batavia St., Orange, CA 92668.

"We learned through our time with Breana that blessings truly come through other people," Frank said. "We want to thank all our family and friends for being there, and the hospital staff. And we're thankful for all the kindness of strangers who reached out to us."